Tightening jacobs chucks

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael-w on 23/01/2017 09:03:11:

… reminds me of the great hammerite debate, nobody so far has taken an old tin of hammerite and a new one and painted the same piece of metal to compare them.

.

It might need a youngster to do that, Michael

Most of us won't live long enough to see an 'old Hammerite' test-piece fail.

… Yes, it really was that good.

MichaelG.

[Bernard WrightParticipant @bernardwright25932]

Everyone has their own preference, whether acquired or impressed upon through training.

I sometimes use more than one pinion hole to try to centralize whatever I'm try to hold, as a rule I only use one hole as in tailstock usage.

Also I use four differing sized drill chucks for appropriate size drills or reamers, as I don't like too much of the jaws extending out of the body, I feel this would produce bellmouthing eventually.

As for the three jaw selfcentring lathe chuck, some people tighten all three, in the past to try to centralize a workpiece, I've used more than one pinion, usually only slightly beneficial, after converting said chuck to 'GripTru', I use only one pinion adjacent to the badge.

I bought a new Pratt Burnerd three jaw chuck, which had on of the pinions marked with a zero, so I use that preferentially.

 

BernardW

 

Edited By Bernard Wright on 23/01/2017 15:37:10

[HacksawParticipant @hacksaw]

Milling cutters need all 3….and then a bit of pipe for extra grippage

Did i say that ?

[EmgeeParticipant @emgee]

Nicholas Farr son of Cooper's man are you he of Farr Formers ? Keep thinking that each time I see your posts, i'm at the opposite side of town.

Emgee

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Emgee, son of the postman actually, but he was a Cooper's man when my eldest sister was born. He of Farr Forms is a cousin of mine and I don't actually live in the town.

Regards Nick.

Edited By Nicholas Farr on 23/01/2017 17:37:09

[oldveloParticipant @oldvelo]

Hi

Thanks Nick Farr for explaining in a clear and concise way what happens in workings of a three jaw chuck read and learn

Eric

[Sam Longley 1Participant @samlongley1]

Posted by Nicholas Farr on 23/01/2017 08:31:15:

This procedure also helps prevent long term permanent distortion of the ring over many operations and puts a much more even load on each jaw.

I cannot see that . The chuck with 3 holes is not going to have the same hole used every time. Therefore, if distortion did occur it would be compensated when a different hole was used the next time an object was placed in the chuck. Over its life there is a fair chance that every hole will be use roughly the same number of times unless it is in a drill press that always stops at the same place. So using one hole to tighten would not cause long term distortion of a jacobs chuck — would it?

[Nigel McBurney 1Participant @nigelmcburney1]

I Have a Black and Decker !/2 inch heavy duty drill which I bought new in 1964 (£25 ) in the days when B &D produced excellent and expensive tools, still have it, it gets occasional use, the chuck has a Jacobs style CVA chuck,still ok though the key handle is a bit curved,in the instructions it stated that the chuck should be tightened by placing the key in each hole in turn to fully tighten the chuck, the only time that I have seen this instruction in writing,how do I remember the cost after all this time,well I was buying through the company where I had been apprenticed at a small discount at 5 shillings a week,then I decided to change jobs so had pay the balance before I left, though the next job soon covered the outlay as there so much overtime.

[not done it yetParticipant @notdoneityet]

I will stick my oar in and suggest that if the whole caboodle was a perfect fit, with no free tolerance anywhere, tightening at any one point would tighten all three jaws to exactly the same degree. So I am in agreement with Neil L.

However, they do have tolerance and are not a perfectly tight fit, either from new or any time therafter. That means that the tightening ring will not engage to exactly the same extent at all points (think here the ring may be tight at the keying point but the ring may not be concentric and have clearance/movement at 180 degrees of exactly the same amount as the ring at the keying point.

If there were 4 jaws to the chuck, the tool would be tightened off centre, but as there are usually 3 jaws, there will be a difference, but obviously at 120 degrees so not quite so obvious (but still there!).

Tightening the ring at each 120 degrees will give an even tightening. That appears to be evidenced by those that observe tightening at progressive points. This is likely to be far more prevalent with a well worn ring, to the point where the drill, or whatever, is not clamped sufficiently unless tightened at each station.

So simply a matter of degree of gears meshing, or not so meshing, on adjacent and opposite sides, I think.

[richardandtracyParticipant @richardandtracy]

Agree with NDIY.

Will further add that I get better concentricity and axial parallelism on my tailstock chuck if I tighten loosely with one hole and then progressively with the next ones. If I tighten only on one hole, can get up to 0.5mm off centre at the tip of a long drill (14mm dia blacksmith's drill). This is of fairly significant concern when drilling into a 15mm OD bar… OK, my tailstock chuck is pretty beaten up and has been heavily used, but when tightened correctly it usually works well. I have occasionally had to substitute an ER32 collet chuck when the drill chuck refuses to co-operate, though.

Regards,

Richard.

[Danny M2ZParticipant @dannym2z]

What is the difference (apart from size) between tightening a 3 jaw drill chuck and a 3 jaw lathe chuck?

I learned (possibly from a Workshop Practice' book) that each chuck has a 'preferred jaw' that gives best concentricity during the final tightening – in the case of my mini-lathe this is #3 jaw. Always better than 0.001" runout on ground stock test pieces.

One of the first jobs that I did when I purchased my mini-lathe was to mark (center-pop) the spindle and the chucks so re-assembly was repeatable if the chuck was removed for other tasks such as rotary table use.

* Danny M *

[Martin KyteParticipant @martinkyte99762]

Thinking in the abstract for a moment if you consider that you trying to produce a symetrical grip on the drill via some mechanism (namely the chuck) intuitively the input force(s) would ideally be symetrical too. Therefor you would think that the ideal way to tighten a chuck with three key positions is with three keys applying the same torque simultaneously.

Practically no-one is going to use three keys. (you would never be able to find a least one of them for a start, it's bad enough keeping track of one key). I would imagine that the only time most people would tighten at all three positions with a single key is to obtain a tighter grip on the drill which may well aid concentricity too as a by product. I'm fairly sure there will be many out there who have tightened a 3 jaw lathe chuck on all three positions to get a better grip.

Incidentally (or maybe pertinently) for a 1/2" heavy duty Jacobs Keyed Chuck selected at random from Jacobs website quotes a runout of 4thou TIR at half capacity.

Question: Is a better distribution of tightening forces one reason why keyless chucks tend to be more accurate than Jacobs chucks.

I would suggest that it may well be good practice to tighten all three positions not least because there is less chance of drills spinning in the jaws and needlessly wearing the chuck. Could this be a question of the right answer but not for the reason you were thinking?

regards Martin

[Sam Longley 1Participant @samlongley1]

Posted by Martin Kyte on 25/01/2017 09:51:27:

Question: Is a better distribution of tightening forces one reason why keyless chucks tend to be more accurate than Jacobs chucks.

Geuine query

Are they?.

I see them on some you tube vids such as Myford boy & I never have any luck with them so wondered why people bother with them

( & no -I will not ask if one grips it in 3 places )

Edited By Sam Longley 1 on 25/01/2017 13:04:45

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Danny M2Z on 25/01/2017 09:49:06:

What is the difference (apart from size) between tightening a 3 jaw drill chuck and a 3 jaw lathe chuck?

.

Danny,

Have a look at the link I posted on page_1of this thread … Whilst there are obvious similarities to the lathe chuck, you will see that the geometry is very different.

I suspect [and it is no more than that] that the drill chuck is less 'predictable' in its behaviour.

MichaelG.

[jaCK HobsonParticipant @jackhobson50760]

Posted by Jon Gibbs on 22/01/2017 09:58:54:

Another thought is whether the number of teeth on the bevel gear of the chuck is divisible by 3.

If it isn't divisible by 3 then there will be a slight mechanical advantage difference between the 3 holes with the same rough key orientation?

Just a thought but perhaps over-thinking it?

Jon

I think that is worth further investigation. Got to find someone who will count and post the results…

[Martin KyteParticipant @martinkyte99762]

In response to Sam, Jacobs do a keyless 13mm drill chuck and quote 0.0015 TIR against 0.005 TIR for the 1/2" heavy duty keyed chuck. I agree it's a little like comparing apples and oranges (or maybe grapefruits and oranges) but my assertion seems to carry some weight.

so –

Question: Is a better distribution of tightening forces one reason why keyless chucks tend to be more accurate than keyed chucks.

I don't know but I would be interested in the response.

regards Martin

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Martin Kyte on 25/01/2017 13:50:52:

Question: Is a better distribution of tightening forces one reason why keyless chucks tend to be more accurate than keyed chucks.

I don't know but I would be interested in the response.

.

Martin,

There is a rather good sectional drawing of the Jacobs keyless precision chuck included here: **LINK**

http://www.jacobschuck.com/keyless-precision-chuck-repair-guide

I would say this supports your hypothesis

There is definitely more 'bearing area' than you would find in a typical keyed chuck.

MichaelG.

[Martin KyteParticipant @martinkyte99762]

You mean the hypothesis that generally they seem to be of better precision?

I had sort of taken that as a given. My hypothesis was that part of the precision comes from a more even distribution of tightening torque which by implication would give weight to the tighten all the holes idea for the keyed chuck.

Usefull link. I cannot see from the illustration what the arrangement is for the jaw guides. Rohm chucks seem to have tiny tee slots.

Getting back to keyed Jacobs chucks keeping the things clean and lubricated would probably solve most peoples needs.

Martin

[richardandtracyParticipant @richardandtracy]

Posted by Martin Kyte on 25/01/2017 15:13:26:

…Getting back to keyed Jacobs chucks keeping the things clean and lubricated would probably solve most peoples needs.

Martin

The best point so far!

Regards,

Richard.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Martin Kyte on 25/01/2017 15:13:26:

You mean the hypothesis that generally they seem to be of better precision?

I had sort of taken that as a given. My hypothesis was that part of the precision comes from a more even distribution of tightening torque …

.

It was your hypothesis, as stated ^^^ that I was attempting to support.

[the strikethrough is mine, just for emphasis]

MichaelG

[not done it yetParticipant @notdoneityet]

I never have any luck with them so wondered why people bother with them

Maybe require a little elaboration on this. Grip or precision? Ease of use? Speed of use? Longevity?

Likely all go hand in hand with quality. And most increase as the item quality rises (along with the cost). Likely the "buy cheap, buy twice" general principle.

More grip likely requires more turns, so there will always be a compromise.

[Michael GilliganParticipant @michaelgilligan61133]

The posts towards the bottom of this page **LINK** may be of interest.

http://www.model-engineer.co.uk/forums/postings.asp?th=124235&p=3#2128649

MichaelG.

[MWParticipant @mw27036]

I can think of a few reasons why a drill would wander off centre, uneven lip length or drilling beyond the maximum movement of the quill with the tailstock in the lathe. These matter much more to the end the result. I have never tightened 3 holes in sequence, and so long as I didn't foul the other problems, I always had a straight hole.

I'm pretty sure I've seen some chucks with 4 tightening holes, so that clearly didn't correspond to the number of jaws. The number 3 has been clearly used to cover the minimum p.c.d to allow for convenient access.

If you're actually getting any movement beyond "hard pressure" you're probably digging into the drill at that point.

You shouldn't need that much force on a drill chuck, if you do then I would rather consider a collet chuck with an all-over grip.

I just worry that theres not really any significant evidence to justify this practice beyond a distant memory? We're supposed to be asking why. Never before today has any experienced engineer I've known done this to a chuck.

By the way, I'm not criticising the use of Jacobs chucks, as I have 5 official Jacobs chucks of differing sizes!

Michael W

Edited By Michael-w on 25/01/2017 22:06:06

[Sam Longley 1Participant @samlongley1]

So after 47 posts( plus a few on another thread) I cannot really see that the forum has come up with an indisputable answer

the question being that the operator rotates a ring with a key. Whether it makes a difference if you rotate that ring from one hole or all 3 is what i wanted to know & why.

Personally I do not think it needs all 3 & nobody has convinced me otherwise yet. Other than saying ( typically) " somebody told me to do it"– & several have said that so far, among some other theories based on concentricity of the ring

& with the greatest of respect to all those that have taken the time & interest to reply, that is not really proof, is it?

But you have to admit it does create a lot if discussion & when i asked it years ago in my works canteen we came to the decision that the practice really boils down to personal preference–

and why not? if that is the way you want to do it, then do it

But thanks for the comments all the same

[SillyOldDufferModerator @sillyoldduffer]

Returning belatedly this morning to my question "How do you tell a poster he's wrong", I found the thread locked, partly because it had picked up some comments on Jacobs Chucks! Thanks to everyone who replied to my question, and for providing a neat link to this thread!

On the subject of Jacobs Chucks I have one that absolutely must be tightened using all three holes. Drills come loose if it's not done, and it was unnecessary when the chuck was new.

Here's photographic evidence of what I think is going wrong

Not too obvious in the photo is that the teeth are worn. Even when new these teeth did not mesh particularly well with the key; over time this has got worse, and the key sometimes rides out..

It can be seen that turning the key has gouged a trench in the body of the chuck. This suggests that tightening the chuck involves misplaced significant force. (And perhaps that the steel of this chuck is soft.) Even more suggestive is damage to the hole itself. Use has enlarged the hole and reshaped it into an oval. It has also developed a noticeable bell-end.

This wear is bad news, because the key no longer seats properly in the hole, and the misplaced torque makes it difficult to tighten the chuck. Pushing the key to close the gap helps, but not much.

It is only possible to tighten this chuck properly by using all three holes progressively.

So I suggest, this is an "it depends" question. It probably doesn't matter if a brand-new well-made chuck is tightened by putting the key in a single hole. As there's no slop, the turning forces are sufficient to tighten the chuck.

But no matter how well-made, that chuck will eventually wear.. Once that starts we have a new situation that gradually comes to dominate. Wear causes the forces applied to the chuck to tilt causing wedging in addition to the desired turning action. Moving the key from hole to hole would tend to break the wedge, and each movement would allow the chuck to nip up further. Now having three holes matters.

My hypothesis is that chucks are provided with three holes to extend their effective lives. A chuck with one hole would wear out quickly. Three holes are better than two when it comes to evening out wear, and four would be a structure weakening overkill.

I suspect but can't prove, that my chuck is also worn on its "axle". It certainly has 'run-out' that might be worse than when new. Again this would cause a tilt tending to increase wedging.

If I was clever enough I'd attempt a mathematical analysis. I'm not! Anyone know if Fusion360 could do it?

Dave

[Author]

Posts